We consider that the R-RIS consists of single-RX-RF Uniform Planar subArrays (UPAs) of meta-atoms and, according to Fig. REF , is placed parallel to the \(y\text{-} z\)  plane. It is also shown in the figure that the outputs of the reception RF chains of all subarrays feed a baseband AoA estimation and localization module, which is part of the R-RIS controller and is based on the extraction of the impinging signal's angular parameters with respect to each subarray, similar to the localization mechanism of multi-anchor systems operating in narrowband transmission conditions [1]}. To this end, the R-RIS controller has basic storage and computing capabilities.It is noted that the proposed baseband AoA estimation and localization module can be a part of the R-RIS. In this case, the R-RIS controller collecting the output signals from the reception RF chains needs to convey them to the AoA estimation and localization module. The impact of the R-RIS partitioning on the position estimation, whose optimization is left for future work, will be investigated in Section REF .
